I'm getting a little tired of covering O'Reilly's comments on God, but I felt like I should mention a few of the other responses he's gotten. Theoretical astrophysicist Ethan Siegel has some very nice answers (complete with illustrations) for Bill's ignorant questions. Late night talk show host Conan O'Brien also had a joke about Bill's line of reasoning:
"Bill O'Reilly said the ocean tides could only be explained by God. Then, when told they were caused by the moon, he said, 'Then how did the moon get there?' In a related story, Bill O'Reilly is a five-year-old boy."
It's funny, but at the same time a little depressing, since that really is roughly his level of discourse on the subject. Finally, Stephen Colbert weighs in again (starting at 2:25 below):
Around the 4-minute mark Colbert points out something I missed—namely, that Bill asked why Earth has a moon and Mars doesn't, but Mars actually has two moons, Phobos and Deimos. The rest is mostly mockery – which is totally okay. When an argument is just too dumb, and the arguer isn't going to be persuaded by reason, that's often the best response.